JP2003193000A - Cover-lay film, its manufacturing method and flexible printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cover-lay film in a flexible printed circuit board (FPC) and the like, which has sufficient adhesive strength and is suppressed as much as possible in oozing out of an adhesive material at an opening portion such as a terminal part or a land part of a circuit pattern. <P>SOLUTION: The cover-lay film 210 comprises a film substrate 200 and, laminated thereon, at least two adhesive layers having a different gelling time, and flow properties of the adhesive layers are graded so as to increase from the film substrate side to the outside according to the difference in the gelling time. The cover-lay film 210 is pasted on the base film 100 and the circuit pattern 120 to give an FPC 300 having sufficient adhesive strength and suppressed as much as possible in oozing out of an adhesive material at an opening part such as a circuit pattern and the like. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coverlay film used for a flexible substrate (FPC) or the like, a manufacturing method thereof, and an FPC.

[0002]

2. Description of the Related Art In FPC, it is generally practiced to form a predetermined circuit pattern on a metal layer (copper foil) portion on the base film side and then attach a coverlay film as a protective film on the upper surface side thereof. It is being appreciated. The coverlay film is usually attached to almost the entire surface of the base film side.However, for the terminal part and part of the land part of the circuit pattern formed near the edge of the board, the Therefore, it is necessary to keep it open.

This relationship is illustrated in FIG.
As in (B). First, as shown in FIG.
A predetermined circuit pattern 12 is formed on the metal layer (copper foil) attached to the base film 10 via the adhesive layer 11. After that, if the cover lay film 20 is attached to the base film 10 and the circuit pattern 12 via the adhesive layer 21, the FPC 30 as shown in FIG. 4B is obtained. At this time, an opening 22 is provided in advance in a portion corresponding to a terminal portion or a land portion of the circuit pattern 12 on the coverlay film 20 side.

[0004]

SUMMARY OF THE INVENTION Such an FPC 30
In the manufacturing of, the coverlay film 20 is attached by using a method such as a vacuum press. At this time, in order to improve the productivity, it is preferable that the adhesive on the coverlay film 20 side has a large flow property and can enter the circuit pattern 12 portion in a short time.

[0005]

However, when an adhesive having a large flow characteristic is used, the penetration (embedding) of the adhesive into the circuit pattern 12 portion is improved, but as shown in FIG. 5 (A), for example. As described above, the adhesive on the coverlay film 20 side flows out (bleeds out) onto the circuit pattern 12, and sometimes an external appearance problem occurs, and sometimes the adhesive 21a that has flowed out causes soldering or post-treatment. There were problems such as making plating difficult and impossible.

On the contrary, when an adhesive having a small flow characteristic is used, the adhesive on the coverlay film 20 side hardly flows out onto the circuit pattern 12 as shown in FIG. There was a problem that a predetermined adhesive strength could not be obtained because the pattern 12 could not be sufficiently entered and a gap δ was partially formed.

The present invention has been made in view of the above circumstances, and basically, the above problems are caused by laminating at least two adhesive layers having different gel times on a film substrate. It is something that should be resolved.

[0008]

According to a first aspect of the present invention, at least two or more adhesive layers having different gel times are laminated on a film substrate, and the flow of the adhesive layers varies depending on the difference in the gel times. A coverlay film is characterized in that it is inclined so that its characteristics increase from the film substrate side to the outside.

According to a second aspect of the present invention, there is provided a method for producing a coverlay film, wherein the gelling time of the adhesive layer is adjusted by the amount of the curing accelerator added to the base resin.

The present invention according to claim 3 is characterized in that the cover lay film according to claim 1 in which an opening portion is provided at an appropriate position is attached to a base film and a predetermined circuit pattern. On the board.

[0011]

1 (A) to 1 (C) show an example of a method for manufacturing a coverlay film according to the present invention. In the figure, 200 is a film base material, 211 is a first adhesive layer, 212 is a second adhesive layer, and 220 is an opening formed in a portion corresponding to a terminal portion, a land portion or the like of the circuit pattern 120.

First, as the film base material 200, a polyimide film or a PET film is used, and FIG.
As shown in FIG. 5, an epoxy-based or acrylic-based adhesive is applied to one surface thereof to provide a first-layer adhesive layer 211. As the adhesive for the first layer, one having a predetermined gelling time (hour) by adding a predetermined amount of a curing agent and a curing accelerator to the base resin is used. And after this,
For example, it is simply dried for an appropriate period to form an adhesive layer having normal flow characteristics (smaller flow characteristics).

Next, as shown in FIG. 1B, an epoxy or acrylic adhesive is applied as the second adhesive layer 212 on the first adhesive layer 211. As the adhesive for the second layer, one which has a predetermined gelling time by adding a predetermined amount of a curing agent and a curing accelerator to the base resin, but which is smaller than the adhesive for the first layer is also used. use. Then, after this, after drying, a pre-baking process which is a heating process is performed. By this treatment, the curing agent and the curing accelerator in both adhesive material materials work, so that the flow characteristics, which is the object of the present invention, increases from the film base material 200 side to the outside, as shown in FIG. 1C. Thus, the cover lay film 210 inclined is obtained.

As shown in FIG. 2A, the cover lay film 210 thus obtained is provided with a base film 100 and a metal layer (copper foil) portion adhered on the film via an adhesive layer 110. By sticking it on the predetermined circuit pattern 120 formed on, the FPC 300 of the present invention as shown in FIG. 2B is obtained.

In this FPC 300, as shown in FIG. 3, there is the second-layer adhesive layer 212 having a large flow characteristic just on the side of the circuit pattern 120, so that the adhesive material satisfactorily flows and is embedded in the circuit pattern 120. Be done. That is, a predetermined adhesive strength can be obtained by sufficiently filling the adhesive material. On the other hand, the opening 220 of the coverlay film 210
In the portion, seepage of the adhesive material is suppressed as much as possible. That is, since the adhesive material of the first layer having a large flow characteristic is embedded in the circuit pattern 120 portion, the amount of flow on the circuit pattern 120 in the opening 220 portion is reduced, and the adhesive material of the first layer has a small flow characteristic. Because it is difficult to flow. In any case, this makes it possible to avoid the space narrowing of the opening 220 portion, which facilitates the post-processing such as soldering and plating.

In the coverlay film 210 as described above, the specific setting method of the gelling time of the first adhesive layer 211 and the second adhesive layer 212 is not particularly limited, but for example, the base resin of each adhesive material is used. This can be dealt with by changing the addition amount of the curing agent or the curing accelerator added to the.

For example, when the same adhesive is used in the first adhesive layer 211 and the second adhesive layer 212, both layers are cured with an appropriate amount of a curing agent with respect to the base resin of the adhesive material. In this case, the amount of the curing accelerator added to the base resin of the second layer adhesive material should be compared with the amount of the curing accelerator added to the base resin of the first layer adhesive material. You can reduce it. Due to this difference in the amount of addition, when pre-baking both adhesive materials together later, the adhesive material in the first layer cures first and the adhesive material in the second layer cures slowly, so the pre-baking treatment period should be set appropriately. For example, the flow characteristics of the second adhesive layer 212 can be easily increased. The gelling time of both adhesive materials can be adjusted not only by adjusting the amount of the curing accelerator but also by combining this with a curing agent. In addition, even if different adhesives are used, it is possible to increase the flow characteristics of the second adhesive layer 212 by adjusting the mixture of curing agents and curing accelerators to provide a difference in gelation time between the two. Is.

<Examples> FPCs (Examples 1 to 3) produced by using a coverlay film satisfying the conditions of the present invention by blending a curing accelerator shown in Table 1 and the conditions of the present invention are lacking. FPC manufactured using coverlay film
Regarding (Comparative Examples 1 to 3), the adhesive strength of the coverlay film and the seepage of the adhesive material into the opening portion were examined. In each of these examples and comparative examples, the film base material of the coverlay film is a polyimide film (25 μm),
The adhesive material (base resin) of the first adhesive layer and the second adhesive layer was an epoxy adhesive, the curing agent was a dicyanamide curing agent, and the curing accelerator was an imidazole curing accelerator. In addition, in Table 1 above, the numerical values of the curing agent and the curing accelerator are
It represents the amount added (parts by weight) relative to 100 parts by weight of the base resin.

Further, in concrete manufacturing, first,
An epoxy-based adhesive having a thickness of 15 μm is applied to the film base material of the coverlay film as a first adhesive layer, left to dry for 2 days, and then an epoxy-based adhesive is used as a second adhesive layer on the first adhesive layer. The adhesive was applied with a thickness of 15 μm. Then, after this, as prebaking, it was left in an oven at 40 ° C. for 2 days. The cover lay film thus obtained was hot-pressed for 2 minutes to form a predetermined circuit pattern on the base film and the metal layer (35 μm) portion attached to the film via the adhesive layer. It pasted and obtained FPC.

The results of the above-mentioned adhesive strength and the exudation of the adhesive material into the openings are also shown in Table 1. The adhesive strength and the seepage of the adhesive material were examined by the following methods.

<Adhesive Strength Test> The cover lay film was peeled off from the base film and the circuit pattern on this film, and the one having a sufficient peeling resistance at that time was passed (○), and the one insufficient was judged to be unsatisfactory. Passed (x).

<Bleeding Test> When the width (groove or hole width) of the opening portion of the cover lay film is 0.2 mm, the case where the adhesive material largely bleeds to the opening side on the circuit pattern is rejected (× ), And the case where the exudation was small was regarded as a pass (◯).

[0023]

[Table 1]

From Table 1 above, in the FPC (Examples 1 to 3) using the coverlay film satisfying the conditions of the present invention,
It can be seen that the adhesive strength and the exudation of the adhesive material are all good (pass).

On the other hand, it is understood that the FPCs (Comparative Examples 1 to 3) using the coverlay film which does not satisfy the conditions of the present invention have a problem in terms of adhesive strength. That is, in Comparative Example 1, since the amounts of the hardening accelerators added to both the first and second adhesive materials are the same and the gelation times of the two are the same, the flow characteristics are small and the embedding in the circuit pattern portion is difficult. Since it is insufficient, it can be seen that sufficient adhesive strength cannot be obtained. Further, in Comparative Example 2, since the amount of the curing accelerator added to both the second-layer adhesive materials is larger than that in the first layer,
It can be seen that the flow characteristics are still small and sufficient adhesive strength cannot be obtained. In Comparative Example 3, it can be seen that sufficient adhesive strength cannot be obtained because there is only the first adhesive layer and the flow characteristics are small.

In the above embodiment, the coverlay film is applied to the single-sided type FPC, but the present invention is not limited to this and can be applied to the double-sided type FPC. Further, in the above-mentioned embodiment, the number of the adhesive layers was two, but the present invention is not limited to this, and the number of adhesive layers is three.
Even if it is a layer or more, the flow property of the adhesive layer may be increased from the film substrate side to the outside.

[0027]

As is clear from the above description, according to the coverlay film of the present invention, at least two adhesive layers having different gel times are laminated on the film substrate, and the gel times are different. Since the flow characteristics of the adhesive layer are inclined so that the flow characteristics increase from the film substrate side to the outside, the adhesive material has sufficient adhesive strength and the adhesive material oozes into the openings such as the terminals and lands of the circuit pattern. It is possible to obtain an excellent FPC in which the temperature is suppressed as much as possible.

According to the method of manufacturing a coverlay film of the present invention, the flow characteristics of two or more adhesive layers can be easily adjusted by adjusting the gelation time of the adhesive layer by the addition amount of the curing accelerator to the base resin. A large coverlay film can be obtained.

According to the FPC of the present invention, the cover lay film having openings such as terminals and lands of the circuit pattern provided at appropriate places is stuck on the base film and the predetermined circuit pattern. , An excellent substrate can be obtained.

[Brief description of drawings]

FIG. 1 is a process drawing showing an example of a manufacturing process of a coverlay film according to the present invention.

FIG. 2 is a plan view showing a case of using a coverlay film according to the present invention.
It is process drawing which showed an example which manufactures PC.

FIG. 3 is an enlarged view of the FPC obtained in FIG.

FIG. 4 is a process drawing showing an example of manufacturing an FPC using a conventional coverlay film.

5 is an enlarged view of each FPC obtained in FIG.

[Explanation of symbols]

100 base film 110 Adhesive layer 120 circuit patterns 200 film substrate 211 First adhesive layer 212 Second adhesive layer 220 openings 300 FPC

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4F100 AK01A AK49 AK53G BA03                       BA10A BA10C BA27 CA02B                       CA02C CA02H CC03B CC03C                       GB43 JL11B JL11C                 4J004 AA10 AA13 AA17 CA06 CC02                       CE01 FA04 FA05                 4J040 DF041 EC001 HC18 HC24                       JA09 KA16 KA17 LA05 NA20                 5E314 AA32 AA33 AA36 BB01 FF06                       GG11

Claims (3)

[Claims] 1. At least two adhesive layers having different gel times are laminated on a film substrate, and the flow characteristics of the adhesive layer are increased from the film substrate side to the outside due to the difference in the gel time. A coverlay film characterized by being inclined. 2. A method for producing a coverlay film, wherein the gelling time of the adhesive layer is adjusted by the amount of a curing accelerator added to the base resin. 3. A flexible substrate, characterized in that the cover lay film according to claim 1 provided with an opening portion at an appropriate position is attached on a base film and a predetermined circuit pattern.